Atrial fibrillation (AF) is the most common cardiac arrhythmia and its prevalence increases with age. The most dangerous and complex arrhythmias are the result of a phenomenon known as reentry. In experimental studies, the vena cava has been associated with ectopic activity that promotes the generation of reentries. The changes caused by electrical remodeling in an atrial myocyte action potential model (AP), coupled with an anatomically realistic three-dimensional model of human atria with orientation fibers were incorporated in this work. When applying an ectopic focus to the nearby ostium of the inferior vena cava, a relationship between this activity and the generation of reentries in the pectinate muscles is found. A functional reentry repeated in time is favored by the pectinate muscles anatomy, the anisotropic properties and the non-uniform distribution in the three-dimensional tissue. The existence of a preferential conduction pathway facilitates the initiation of reentries affecting the conduction scheme. Therefore, the capacity of induction and development of arrhythmias are found.